A gas expander is used for the purpose of sucking a high-pressure gas discharged from a plant, and expanding it to convert the pressure energy of the gas into velocity energy (mechanical energy), thereby recovering power, and decreasing power of a drive motor or the like. This is well known from Patent Document 1, etc.
There may be a case where the gas expanders need to be provided in multiple stages in order to accommodate (absorb) a high pressure ratio or achieve high performance. In this case, a radial gas expander of a geared type (speed increasing gear type) as shown, for example, in FIG. 4 is conceivable (see Patent Document 2).
According to this radial gas expander, an expander wheel shaft 102 is supported by a gear casing 100 via bearings 101A. Also, a plurality of expander pinion shafts (impeller shafts) 103 parallel to the expander wheel shaft 102 are supported by the gear casing 100 via bearings 101B. Expander impellers (impeller vanes) 104 of high-pressure stages A, B and C, D are arranged at both ends of one of the illustrated expander pinion shafts 103, while expander impellers (impeller vanes) 104 of low-pressure stages E and F are arranged at both ends of the other expander pinion shaft 103.
In each stage, a high-temperature high-pressure gas discharged from a plant is sucked toward the expander impellers 104 from an inflow casing 105 constituted as a spiral casing, and guide vanes (nozzle blades) 107 provided in a disk-shaped annular space 106. Thus, the gas is expanded, and discharged from an outlet conical diffuser 108. Power recovered by sucking and expanding the gas is transmitted to the expander wheel shaft 102 via a gear train to decrease the power of a drive motor or the like (not shown). On the one expander pinion shaft 103, the gas exiting from the first-stage expander impeller 104 is sucked into the second-stage expander impeller 104 via a return ring (return bend) 109 so that the suction and expansion process for the gas is repeated in the two stages.